Intravascular brachytherapy delivered at the time of angioplasty has been proven to be effective in preventing restenosis induced by interventional recanulazation procedures. The overall objective of this proposed project is to improve the efficacy of intravascular brachytherapy with minimized associated toxicity, by exploring the use of various isotopes. The scheme proposed in this project to improve the treatment efficacy and to decrease the risk of late tissue damage is to optimize the dosimetry by exploiting different isotope characteristics so that highly localized radiotherapy can be delivered with minimal toxicity to surrounding normal tissue. The specific approaches are: (1) To determine the accurate and precise dose distributions of 90Sr, 90Y, 125I and 192Ir sources. (2) To explore potential beta emitters, 106Ru/Rh and 144Ce/Pr, by assessing their dose distributions, within the target cells as well as adjacent non-target normal tissues using dosimetric methods in microscopic scale. We will perform precision dosimetric studies for these radionuclides (a) in homogeneous tissue equivalent medium and (b) with heterogeneities present in the vessel, such as blood, contrast medium, calcified plaque and stainless steel stents. Two complementary means will be employed: (a) measurement using a new type of x-ray film, called GafChromic film, and (b) calculations using a Monte Carlo simulation code, MCNP. The effect on the dose distributions by the heterogeneities will be studied and quantified. We will devise an improved methodology of treatment planning calculations to incorporate the dose modifying functions for general shape and dimensions of the heterogeneities.